The present invention is directed to a marine platform structure, and particularly to a semisubmersible trimaran with an upper deck supported on a center hull and column-stabilized outrigger pontoons.
It has been proposed to use large marine platform structures as one component in an afloat sea base comprising perhaps a dozen other specialized structures and/or vessels. The marine platform structure would contribute to the capabilities of the afloat sea base in providing logistics and basing functionality, e.g. cargo transfer and warehousing facilities, fuel and water storage, aircraft landing and takeoff facilities, marine vessel and aircraft repair facilities, vehicle storage and repair facilities, personnel housing, hospital, off-shore basing for security operations, and the like.
Such a structure must be deployable to a stationing location at a reasonable transit speed, and yet must be able to stay in position with low motion characteristics in variable wind, wave, and weather conditions. The structure must be stable both during transit and in operation.
Semisubmersible marine structures are well known in the oil and gas industries. Such structures are typically only moveable by towing. These semisubmersibles have a relatively low transit draft that allows them to be floated to a stationing location, where they can add ballast, usually by taking on seawater, to assume a relatively deep draft or semisubmerged condition for operation.
Flotation of semisubmersibles is usually accomplished with pontoons on which an upper deck is supported by columns. The pontoons provide a relatively large waterplane area, as is desirable for transit, but when submerged for stationing, the columns connecting the pontoons to the upper deck present a lower waterplane area for operation. The low waterplane area is desirable to reduce motion characteristics from waves, especially during swell seas and storms. The upper deck from which rig activities are conducted must be maintained above the water plane at all times.
U.S. Pat. No. 5,823,130 to Kreyn et al. discloses a catamaran or trimaran-style vessel for shipping a combination of liquids and containerized cargo. Two or three longitudinal hull sections providing internal tanks for storage of liquids are connected by a deck surface on which to stack cargo containers.
Small waterplane area tri-hull ships or SWATH vessels, have been used as ferries for cars and passengers, cruise vessels, oceanographic research, patrolling, and other off-shore crew service functions. The SWATH acronym has also been applied in trade terminology to twin-hull vessels. Some 50 commercial SWATH vessels have been placed in service worldwide, with displacements typically below 1,000 tons. However, there is a SWATH cruise ship having a displacement of about 11,500 tons.
A SWATH type ship for use in cleaning oil-slicks is currently being developed by Alstom. The trimaran features a large slender central hull, and two lateral stabilizing hulls. Oil is collected from the surface of the water between the hulls, where the area between the hulls is protected from the current allowing stabilization for improved collection. The ship is designed to operate in gale force conditions and can hold up to 6000 metric tons of collected oil.
U.S. Pat. No. 6,550,408 to Janssen discloses methods and apparatus for more economically loading/unloading cargo from a multi-hull ship. Janssen teaches a design of SWATH ships having no interior cargo holds, arid using surfaces of a segmented, submersible platform for stowing floatable cargo.
U.S. Pat. No. 6,378,450 to Begnaud et al. discloses a towed, semi-submersible, twin-hull pontoon structure with four corner caisson columns. The caissons are connected by horizontal braces to reduce spreading and torque-inducing forces. The structure can support an off-shore drilling unit for use in moderate or severe conditions, employing thruster assemblies for dynamic station keeping.
U.S. Pat. No. 6,374,764 to Davenport et al. discloses an apparatus and method for installing a deck on an off-shore substructure, such as for example, a drilling station for oil or gas production. The patent discloses a self-floating apparatus with pontoons which support a self-jacking deck.
U.S. Pat. No. 6,341,573 to Buck provides a ship able to be converted into a floating aircraft runway, supported on slender, buoyant hull/spar legs that pivot downward from a retracted horizontal configuration to a vertical configuration. Multiple vessels are connected together for stationing.
U.S. Pat. No. 3,939,790 to Varges et al. and U.S. Pat. No. 4,147,123 to Kirby et al. disclose flotation methods and monohull ship designs for loading and unloading floatable cargo such as barges.
U.S. Pat. No. 6,532,884 to Profitt et al. discloses designs for various high-speed watercraft, driven by electric motors. The designs generally relate to small craft, such as for example pleasure boats, featuring a submersible center hull and two adjacent, floatable skis on adjustable struts vertically moveable to control the hull submersion.